GB649983A - Extractive distillation process - Google Patents

Abstract

<PICT:0649983/III/1> Two components or groups of components of a mixture are separated by submitting the mixture to extractive distillation using two liquids A and B and operating so that only a single liquid phase is present in the distillation zone; the liquid (B) of lower overall solvent power for the components is chosen so as to have greater solvent selectivity for one component or group than has the other liquid (A), and at least part of liquid (B) is introduced into the distillation zone below the inlet of liquid (A). The vapour withdrawn from the distillation zone is rich in one component or group while the extract is a solution of the other component or group in both liquids (A) and (B). Examples of mixtures which may be separated are: cyclohexane and trimethylbutane, methylcyclopentane and n-hexane, methylcyclohexane and n-heptane, cyclopentane and dimethylbutane, toluene and dimethylhexane, toluene and methylcyclohexane, butadiene and butene, n-butane and n-butenes, phenols and thiophenols, fatty acids having different degrees of unsaturation such as oleic, linoleic and linolinic acids, allyl alcohol and propyl alcohol, ethyl alcohol and crotonaldehyde, butadiene and ethyl chloride, ethylene glycol and diethylene glycol diethyl ether. Suitable pairs of liquids for the separation of hydrocarbons are: acetone and water, dimethylsulpholane and water, phenol and water, aniline and water, cresol and phenol, dimethylaniline and aniline. Relatively non-polar substances may be separated using acetone and dimethyl phthalate, or acetone and ethylene glycol. There should be at least about 2 parts by weight of liquid (B) for every 98-100 parts of liquid (A); and the weight of both to that of the distilland should be between 1 : 1 and 10 : 1. A feed mixture of narrow boiling range containing C4 paraffins and olefines is vaporized and fed, under superatmospheric pressure if desired, through line 11 into column 12. Acetone is admitted to the column through line 14; and water is admitted through line 17 and any one or all of lines 19, 20, 21. If desired a portion of the water may also be admitted through line 14. Paraffin vapours flow over partial condenser 15 and leave the column overhead; they are condensed in condenser 22, and the condensate is separated as an upper layer from entrained extracting liquid in separator 24. The extracting liquid is returned to the column through lines 25, 26 and any one or all of lines 14, 19, 20, 21. The solution withdrawn from the base of column 12 through line 30 is passed to column 31 where the olefines are vaporized and pass overhead to condenser 32. Water is taken off from column 31 through line 37 and is returned to column 12 via line 26. Acetone is taken off from column 31 through line 38 and is returned to column 12 through line 14. Specification 563,930 is referred to.